Method for the preparation of phytosterols from tall oil pitch

ABSTRACT

A method of preparing phytosterols from tall oil pitch containing steryl esters comprises the steps of converting the steryl esters to free phytosterols while in the pitch to produce a modified pitch containing the free phytosterols; removing light ends from the modified pitch by evaporation to produce a bottom fraction containing the free phytosterols; evaporating the bottom fraction to produce a light phase distillate containing the free phytosterols; dissolving the light phase distillate in a solvent comprising an alcohol to produce a solution containing the free phytosterols; cooling the solution to produce a slurry with the free phytosterols crystallized in the slurry; and, washing and filtering the slurry to isolate the crystallized phytosterols.

FIELD OF THE INVENTION

The present invention relates to a method of preparing phytosterols fromtall oil pitch, including the use of distillation techniques to isolatea phytosterol concentrate that can by crystallization yield high purityphytosterols using a solvent comprising alcohol or a combination ofalcohols, and that may include water.

BACKGROUND TO THE INVENTION

Tall oil pitch is obtained from the black liquor of alkaline digestionof coniferous wood, most notably the kraft process. The black liquor istypically concentrated and settled to yield soap skimmings that containsodium salts of fatty acids, sodium salts of resin acids andunsaponifiables. The latter group of substances include fatty alcohols,free sterols, steryl esters, and fatty acid esters. In kraft pulp mills,the collected soap is routinely acidulated with a mineral acid such assulphuric acid to yield an oil phase and a water phase. The oil phasecontains free fatty acids, resin acids and unsaponifiables; it iscommonly known as crude tall oil. Typically, the amount ofunsaponifiables can range from 10 to 35% by weight of the crude talloil, depending on the species and quality of coniferous wood used. Thewater phase containing sodium sulphate and any lignin entrained in theoriginal soap is normally recycled back to the pulp mill chemicalrecovery system. In the subsequent recovery of desired fatty acids andresin acids, crude tall oil is typically evaporated under low pressureconditions to yield a light phase, known as depitched tall oil,containing mainly fatty acids and resins, and a heavy phase, known astall oil pitch, containing a small amount of fatty and rosin acids and asubstantial amount of the original unsaponifiables.

Phytosterols can be isolated from either tall oil soap (sometimesreferred to as soap skimmings) or from tall oil pitch. It is understoodthat the manufacture of sterols from tall oil soap has been practicedcommercially by Oy Kaukas AB, Lppeenranta, Finland since 1981. Thetechnologies are those based on the refining of tall oil soap with acombination of low molecular weight ketones, alcohols and hydrocarbons;for example, as disclosed by Holmbom et al. in U.S. Pat. No. 3,965,085granted on 22 Jun. 1976. The refined tall oil soap is then extracted andcrystallized using a combination of polar and non-polar solvents, forexample, as taught by Johansson et al. in U.S. Pat. No. 4,044,031granted on 23 Aug. 1977 and Hamunen in U.S. Pat. No. 4,422,974 grantedon 27 Dec. 1983. Those methods of manufacture of pure tall oil sterolsrequires the soap skimmings to be relatively free of entrained blackliquor and the use of multiple solvents which entails several separatesolvent recovery systems. The adjustment of precise solvent compositionsto maintain optimal operation for each processing stage is complex. InU.S. Pat. No. 4,153,622 granted on 8 May 1979, Lamminkari et al.disclose the use of acetone and activated carbon to extract sterols fromtall oil soap, in which the acetone extract is subsequently evaporatedfor dissolution in ethanol for the final recovery of sterols.

The recovery of sterols from tall oil pitch has been studied for manyyears. In U.S. Pat. No. 2,715,638, Albrecht et al. teach the use of anamount of dilute alkaline solution to neutralize the fatty and rosinacids in tall oil pitch but in an amount to saponify the sterol ester.The remaining organic phase is then separated and saponified with analcoholic alkaline solution to convert steryl esters into free sterolsfor subsequent dilution in hot water to precipitate the sterols bycooling. The product purity was indicated to be in the range of 83%. InU.S. Pat. Nos. 3,691,211 and 3,840,570 Julian teaches the use of amixture of alcohol, water and hydrocarbon to extract tall oil pitch,then saponify the hydrocarbon phase with an alkali metal base, andfinally dissolve the saponified material in a polar solvent for therecovery of phytosterols. The procedure is cumbersome as it involvesseveral solvent extraction steps with different polar and non-polarsolvents. The solvent recovery systems for at least polar and non-polarsolvents are complex.

In U.S. Pat. No. 5,097,012 granted on 17 Mar. 1992, Thies et al.disclose a method for the isolation of sterols from crude tall oil bywater extraction at elevated temperatures and pressures.

In U.S. Pat. No. 3,943,117 granted on 9 Mar. 1976, Force discloses aprocess for saponifying tall oil pitch in which a water-soluble cationicamine is used in conjunction with an alkali. In U.S. Pat. No. 4,524,024granted on 18 Jun. 1985, Hughes teaches the hydrolysis of tall oil pitchat elevated temperatures to increase the recovery of fatty acids fromtall oil pitch. In U.S. Pat. No. 3,887,537 granted on 3 Jun. 1975,Harada et al. disclose the recovery of fatty acids and rosin acids fromtall oil pitch by first saponifying tall oil pitch with an alkali metalbase and a low molecular weight alcohol, and then introducing thereacted mixture into a thin film evaporator to remove low-boiling mattersuch as water, alcohol use and light unsaponifiables. The bottomfraction from the first evaporator is next fed to a second thin filmevaporator in which the unsaponifiables including sterols are removed asthe light ends and a molten soap is recovered as the bottom fraction.Fatty acids and rosin acids are recovered from the molten soap fractionby acidulation conventionally with a mineral acid. In U.S. Pat. No.3,926,936 granted on 16 Dec. 1975, Lebtinen teaches the recovery offatty acids and rosin acids from tall oil pitch by reacting tall oilpitch with an alkali at 200 to 300 degrees Celsius, in the amount of 5to 25% of tall oil pitch, prior to vacuum distillation of the heatedmixture to recover the fatty acids and rosin acids in the distillatefraction.

SUMMARY OF THE INVENTION

In a broad aspect of the present invention there is provided a new andimproved method of preparing phytosterols from tall oil pitch containingsteryl esters, the method comprising the steps of:

-   -   (a) converting the steryl esters to free phytosterols while in        the pitch to produce a modified pitch containing the free        phytosterols;    -   (b) removing light ends from the modified pitch by evaporation        to produce a bottom fraction containing the free phytosterols;    -   (c) evaporating the bottom fraction to produce a light phase        distillate containing the free phytosterols;    -   (d) dissolving the distillate in a solvent comprising an alcohol        to produce a solution containing the free phytosterols;    -   (e) cooling the solution to produce a slurry with the free        phytosterols crystallized in the slurry; and,    -   (f) washing and filtering the slurry to isolate the crystallized        phytosterols.

Preferably, the step of converting the steryl esters to freephytosterols comprises the steps of saponifying the tall oil pitch withan alkali metal base, neutralizing the saponified pitch with an acid,and heating the neutralized pitch to remove water. The resulting pitchwith such water removed defines the modified pitch.

BRIEF DESCRIPTION OF THE DRAWINGS

The FIGURE shows a schematic flow diagram for the preparation of highpurity phytosterol crystals from tall oil pitch in accordance with thepresent invention.

DESCRIPTION OF PREFERRED EMBODIMENT

In accordance with the present invention, the isolation of phytosterolsfrom tall oil pitch first requires converting steryl esters present inthe pitch to free phytosterols while in the pitch. The result is amodified pitch containing free phytosterols.

It is contemplated that the required conversion may be accomplished byvarious methods. In the FIGURE, the conversion step is indicated byblock 30 (shown in broken outline) which receives an incoming feed oftall oil pitch 1 and produces modified pitch 11 as an output. Thepresently preferred method of conversion involves the use of an alkalibase treatment and is indicated by the elements contained within block30.

As depicted within block 30, tall oil pitch 1 is added with an alkalimetal base 2 into a reactor 3. The amount of alkali metal base relativeto the tall oil pitch preferably should be sufficient to facilitatesubstantially complete saponification of the tall oil pitch.

Cost effectiveness considerations will generally favor the use of awater solution of s an alkali metal base such as sodium hydroxide,potassium hydroxide or a combination thereof. These compounds orcombinations will provide a relatively high alkalinity for a relativelyreasonable cost. If such compounds or combinations are used, then thestoichiometric proportion of alkali metal base 2 to tall oil pitch 1that theoretically is required to achieve complete conversion typicallymay be in the neighborhood of about 1% by weight. Of course, the preciseamount will depend upon the specific characteristics of tall oil pitch1, and these characteristics may vary from one batch of feed or sourceto another. As well, and again depending upon the specificcharacteristics of tall oil pitch 1, it will be recognized that asignificant portion of alkali metal base 2 may be consumed by reactionwith constituents of pitch 1 other than steryl esters. Accordingly, toprovide a strong driving force for the reaction, and to better ensureefficient conversion of the steryl esters that are present, asignificantly higher proportion of alkali metal base 2 to tall oil pitch1 may be considered desirable. Typically, this proportion may be in therange of 5 to 15% by weight.

Mixing is sustained in reactor 3 with sufficient to vigor to maintaincontact between pitch 1 and alkali metal base 2. Typically, an operatingtemperature in the range of 100 to 250 deg. C. for a period in the rangeof 60 minutes (at the higher temperature) to 300 minutes (at the lowertemperature) will suffice to facilitate the desired saponification.

Following saponification in reactor 3, the saponified pitch 4 isdischarged into a second reactor 6. An acid 5 is also added to reactor6.

Acid 5 may be a simple organic acid such as acetic acid or formic acid,both of which are commercially practical. As well, acid 5 may be amineral acid such as sulphuric acid, hydrochloric acid or phosphoricacid. These are relatively strong mineral acids and are favored overweaker acids such as boric acid. Nitric acid is a possibility. However,it is contemplated that undesirable nitration may occur.

Sufficient acid 5 is added to reactor 6 such that the mixture reaches awater phase pH between 4 and 7, and preferably between 5 and 7. Althoughthe mixture should be monitored during the additive process, the lattertypically will be achieved when the amount of acid is about 20% inexcess of the stoichiometric amount required for the neutralization ofthe residual alkali metal base present in saponified pitch 4.

With gentle stirring in reactor 6, an operating temperature in the rangeof 10 to 100 deg. C. for a period in the range of 1 hour (at the highertemperature) to 10 hours (at the lower temperature) will typicallysuffice to facilitate the desired neutralization. Then, with continuedgentle stirring, the mixture in reactor 6 is maintained at a temperatureof about 95 deg. C. for approximately 120 minutes to effect the bulkdisengagement of water from the organic phase. Excess water 7 is drawnoff and the resulting neutralized pitch 8 is introduced into a thirdreactor 9 for further processing.

Notwithstanding the removal of excess water 7 in reactor 6, a relativelyhigh water content may still subsist By heating mixture 8 in reactor 9,preferably under vacuum conditions, water 10 is further stripped off toproduce a modified pitch 11 containing free phytosterols and preferablycomprising less than 1% by weight water.

Modified pitch 11 is introduced into an ultra-low pressure evaporator 12operating in the range of 0.1 to 10 millibars pressure (but preferablynot more than 1 millibar) and at a temperature in the range of 160 to280 deg. C., for the removal of 1 to 15% of light ends 13 in themodified pitch. These light ends will comprise a high proportion of thefatty and resin acids found in the original tall oil pitch 1.

The bottom fraction 14 of modified pitch 11 contains the freephytosterols and is removed from evaporator 12 and introduced into asecond ultra-low pressure wiped film evaporator 15. Evaporator 15 servesto distill free phytosterols present in fraction 14 into a light phasedistillate 16. To do so efficiently, it preferably is operated at apressure in the range of 0.01 to 1.0 millibars pressure and at atemperature in the range of 180 to 300 deg. C. Distillate 16 alsocontains fatty alcohols, fatty acids, rosin acids and high molecularweight wax esters. A bottom fraction 17 is discarded and may be used asa waste fuel or feedstock for other industries.

Distillate 16 is introduced into a further reactor 18 where it is heatedand stirred until dissolution has occurred in an added solvent 21.Solvent 21 includes alcohol, preferably a low molecular weightmonohydric alcohol such as methanol, ethanol or 2-propanol, or acombination of such alcohols. As well, the solvent may include water.

Effective dissolution of free phytosterols has been found to occur atabout 65 deg. C. Other temperatures may of course be used, but it has tobe borne in mind that the solubility of the phytosterols will decreaseas the temperature is lowered

When dissolution has occurred, the solution is cooled in reactor 18together with high speed mixing to produce a slurry 19 with freephytosterols crystallized in the slurry. Typically, the temperature atwhich crystallization is effected may be in the range of 0 to 35 deg. C.

The cooled slurry 19 is washed and filtered to dryness with a filtrationapparatus 20 advantageously using added solvent 21 like that used inreactor 18. The result is a yield of high purity phytosterol crystals 22and spent solvent filtrate 23, the latter of which may be recovered forrecycling and reuse.

In more detail, the practice of the invention may be seen from thefollowing examples:

EXAMPLE 1

9,598 kg of tall oil pitch were saponified with 1,325 kg NaOH at 12.0%concentration solution, at 146 deg. C. for 120 minutes, under vigorousmixing conditions. The weight ratio of sodium hydroxide (dry basis) totall oil pitch was 0.138. The reacted mixture was then neutralized with1,188 kg of 85% concentration phosphoric acid. After continued heatingat 146 deg. C. and gentle stirring for 210 minutes, 6,600 kg of waterwas drawn off from the bottom of the reactor. The pH of the reactorbottom water was 6.4. The partially dewatered mixture containing about37.5% water was transferred to a second reactor for vacuum stripping ofresidual moisture. The vacuum reactor was operated at 149 deg. C. at anaverage pressure of 300 mm Hg. The reaction was completed in 300minutes. The dried, saponified and neutralized tall oil pitch had amoisture content of 0.4% by wt.

Table 1 summarizes the percentage of phytosterols present in free format various stages in the procedure. TABLE 1 Processing Stage %phytosterols in free form Tall oil pitch feed 26.8 After saponification83.0 After neutralization 81.0 After vacuum stripping 84.6

The phytosterols mostly in free from are now ready for separation fromthe modified tall oil pitch.

EXAMPLE 2

A sample of tall oil pitch was saponified, neutralized and dewatered bythe method described in Example 1. The modified tall oil pitch was foundto have a composition of 141 mg free phytosterols/g and 164 mg totalphytosterols/g. The modified tall oil pitch was preheated to about 100deg. C. for feeding into a series of 0.1 square meter wiped evaporators(manufactured by UIC GmbH, Germany). The distillate from eachevaporation stage was recovered for the analysis of free phytosterols bygas-liquid chromatography (GLC).

Table 2 summarizes free phytosterol production results for four testsruns (A1, A2, A3 and A4) under differing conditions of feed rate,temperature and pressure. TABLE 2 Test Number A1 A2 A3 A4 Stage 1Evaporation Tall oil pitch feed, kg/hr 15.5 15.6 11.5 15.6 Temperature,deg. C. 225 225 225 220 Pressure, mbar 5.94 6.53 6.45 2.08 Distillateyield, % by wt. <1 <1 <1 1.90 Free phytosterols in Stage 1 18 18 18 18distillate, mg/g Stage 2 Evaporation Feed from above Stage 1 residue,15.6 15.6 11.5 15.3 kg/hr Temperature, deg. C. 251 269 252 265 Pressure,mbar 0.32 0.37 0.07 0.07 Distillate yield, % by wt. relative 40.4 49.749.6 51.2 to Stage 1 feed Free phytosterols in Stage 2 248 250 254 262distillate, mg/g Free phytosterols recovered in 71.1 88.1 89.4 94.8Stage 2 distillate, % of free phytosterols present in tall oil pitch

EXAMPLE 3

Samples of Stage 2 distillate from Example 2 were crystallized inlaboratory jar tests by heating the distillate-solvent mixture to 65deg. C. The mixtures were cooled to 30 to 35 deg. C. to yield a slurrycontaining the desired phytosterol crystals. The weight ratio of organicsolvent to distillate was 15:1.0. The cooled slurry was then filteredthrough 50 micrometer filter paper, under vacuum. The filtered cake wasthen washed twice with solvent in an amount equal to 1.5 times theweight of distillate sample used for crystallization. The wash solventhad the same composition as that used for crystallization. Washing ofthe cake was conducted at ambient temperature. The washed cake was thendried at 90 deg. C. for 60 minutes prior to weighing and GLC analysis.

Table 3 comparatively summarizes crystal purities and crystal yields fortest runs A1, A2, A3 and A4, firstly, utilizing methanol as the solventand, secondly, utilizing a mixture of methanol and 2-propanol as thesolvent. TABLE 3 Stage 2 Distillate Test Number A1 A2 A3 A4 Solvent:100% methanol Crystal purity, mg pure phytosterols/g dry 983 970 956 933cake Crystal yield, % based on phytosterols in 41.9 43.2 46.3 48.0 testdistillate Solvent: 70% methanol and 30% 2-propanol Crystal purity, mgpure phytosterols/g dry 1000 972 997 997 cake Crystal yield, % based onphytosterols in 30.5 31.9 33.8 38.6 test distillate

EXAMPLE 4

A sample of Stage 2 distillate from Test Number A4 was re-distilledfurther in a wiped film evaporator. The distillate feed had acomposition of 262 mg free phytosterols/g and 264 mg totalphytosterols/g. The feed was pre-heated to about 100 deg. C. for feedinginto the 0.1 square meter wiped film evaporator (manufactured by UICGmbH, Germany). The distillate samples were recovered for the analysisof free phytosterols by gas-liquid chromatography (GLC).

Table 4 summarizes free phytosterol production results for four testsruns (B1, B2, B3 and B4) under differing conditions of feed rate,temperature and pressure. TABLE 4 Test Number B1 B2 B3 B4 Distillatefeed, kg/hr 8.7 8.7 15.1 14.9 Temperature, deg. C. 216 230 240 249Pressure, mbar 0.16 0.15 0.29 0.26 Distillate yield, % by wt. 74.4 85.679.8 86.4 Free phytosterols in distillate, mg/g 248 275 260 266 Freephytosterols recovered 70.7 91.2 80.4 88.4 from distillate feed, % bywt.

EXAMPLE 5

Distillate samples from Example 4 were collected for laboratory scalecrystallization using the procedure described previously in Example 3.The solvent used was 100% methanol. Table 5 comparatively summarizescrystal purities and crystal yields for test runs B1, B2, B3 and B4.TABLE 5 Stage 3 Distillate Test Number B1 B2 B3 B4 Crystal purity, mgpure phytosterols/g dry 992 972 986 978 cake Crystal yield, % based onphytosterols in test 36.9 40.7 37.9 44.8 distillate

EXAMPLE 6

Distillate from Stage 3, distillation Test Number B4, was crystallizedusing other mixtures of alcohol or alcohol and water. The test procedurewas identical to that described in Example 3. The free phytosterolcontent of test distillate was 266 mg/g.

Table 6 comparatively summarizes crystal purities and crystal yields forfive test runs C1, C2, C3, and C4. TABLE 6 Stage 3 Distillate Test No.B4 C1 C2 C3 C4 Methanol, % by wt. 15.0 12.6 70 58.7 Ethanol, % by wt.85.0 71.3 0.0 0.0 2-propanol, % by wt. 0.0 0.0 30.0 25.1 Water, % by wt.0.0 16.1 0.0 16.2 Crystal purity, mg pure phytosterols/g 999 985 991 975dry cake Crystal yield, % based on phytosterols 34.4 46.3 39.1 58.0 intest distillate

EXAMPLE 7

Distillate from Stage 3 distillation Test Number B4 was againcrystallized in the laboratory using alcohols, and the test procedurewas again identical to that described in Example 3, except that thecrystallization was conducted at 0 deg. C. The weight ratio of organicsolvent to distillate was varied. Wash solvent was maintained at ambienttemperature. The free phytosterol content of test distillate was 266mg/g.

Table 7 comparatively summarizes crystal purities and crystal yields fortwo test runs D1 and D2 utilizing the same methanol-ethanol solvent, butwith different proportions of solvent to distillate. TABLE 7 Stage 3Distillate Test No. B4 D1 D2 Methanol, % by wt. 15.0 15.0 Ethanol, % bywt. 85.0 85.0 Proportion of solvent to distillate, by wt. 1.6 3.0Crystal purity, mg pure phytosterols/g dry cake 983 965 Crystal yield, %based on phytosterols in test distillate 66.3 66.6

As noted above, it is contemplated that the conversion of steryl esterspresent in tall oil pitch 1 to free phytosterols while in the pitch maybe accomplished by various methods. The method described involves theuse of an alkali base treatment. Although experimentation may berequired, and although there may be difficulties, other methods that maybe tried include water hydrolysis treatment and acid hydrolysistreatment of the tall oil pitch.

1. A method of preparing phytosterols from tall oil pitch containingsteryl esters, said method comprising the steps of: (a) converting saidsteryl esters to free phytosterols while in said pitch to produce amodified pitch containing said free phytosterols; (b) removing lightends from said modified pitch by evaporation to produce a bottomfraction containing said free phytosterols; (c) evaporating said bottomfraction to produce a light phase distillate containing said freephytosterols; (d) dissolving said light phase distillate in a solventcomprising an alcohol to produce a solution containing said freephytosterols; (e) cooling said solution to produce a slurry with saidfree phytosterols crystallized in said slurry; and, (f) washing andfiltering said slurry to isolate said crystallized phytosterols.
 2. Amethod as defined in claim 1, wherein said modified pitch comprises lessthan 1% water by weight.
 3. A method as defined in claim 1 or 2, whereinsaid solvent comprises a low molecular weight monohydric alcohol.
 4. Amethod as defined in claim 1 or 2, wherein said solvent comprises a lowmolecular weight monohydric alcohol and water.
 5. A method as defined inclaim 1 or 2, wherein said slurry is washed and filtered using a solventlike said solvent used to dissolve said light phase distillate.
 6. Amethod as defined in claim 1, wherein said step of converting saidsteryl esters to free phytosterols comprises the steps of: (a)saponifying said tall oil pitch with an alkali metal base; (b)neutralizing said saponified pitch with an acid; and, (c) heating saidneutralized pitch to remove water, the resulting pitch with such waterremoved defining said modified pitch.
 7. A method as defined in claim 6,wherein said alkali metal base is selected from the group consisting of:(a) sodium hydroxide; (b) potassium hydroxide; (c) sodium hydroxide andpotassium hydroxide.
 8. A method as defined in claim 7, wherein in theweight percentage of alkali metal base to tall oil pitch is in the rangeof 1% to 15%.
 9. A method as defined in claim 7, wherein saidsaponification is conducted at a temperature in the range of 100 to 250deg. C. for a period in the range of 60 to 300 minutes.
 10. A method asdefined in claim 6, wherein said acid is an organic acid.
 11. A methodas defined in claim 6, wherein said acid is a mineral acid.
 12. A methodas defined in claim 11, wherein said mineral acid is selected from thegroup consisting of: (a) sulphuric acid; (b) hydrochloric acid; (c)phosphoric acid; (d) a combination of acids comprising two or more ofsulphuric acid, hydrochloric acid and phosphoric acid.
 13. A method asdefined in claim 6, wherein said neutralization is conducted at atemperature in the range of 10 to 100 deg. C. for a period in the rangeof 1 to 10 hours.
 14. A method as defined in claim 6, wherein saidneutralized pitch has a water phase pH in the range of 4 to
 7. 15. Amethod as defined in claim 6, wherein said heating step comprisesheating at a temperature in the range 90 to 100 deg. C. for a timesufficient to effect the bulk disengagement of water from the organicphase.
 16. A method as defined in claim 15, wherein said heating stepfurther comprises heating under vacuum conditions such that saidmodified pitch comprises less than 1% water by weight.
 17. A method asdefined in claim 1 or 6, wherein said light ends are removed in a wipedfilm evaporator operating at a pressure in the range of 0.1 to 10millibars and at a temperature in the range 160 to 280 deg. C.
 18. Amethod as defined in claim 1 or 6, wherein said bottom fraction isevaporated in a wiped film evaporator operating at a pressure in therange of 0.01 to 1.0 millibars and at a temperature in the range 180 to300 deg. C.
 19. A method as defined in claim 6, wherein said solventcomprises a low molecular weight monohydric alcohol.
 20. A method asdefined in claim 6, wherein said solvent comprises a low molecularweight monohydric alcohol and water.
 21. A method as defined in claim 1or 6 in which the crystallization of phytosterols is effected at atemperature in the range of 0 to 35 deg. C.
 22. A method as defined inclaim 1, further including the step of evaporating said light phasedistillate after step (c) and before step (d) to enhance theconcentration of free phytosterols in said light phase distillate.
 23. Amethod as defined in claim 22, wherein water is added in step (d) in aproportion up to 35% by weight relative to the organic solvent phase.24. A method as defined in claim 23, wherein the weight ratio of solventto distillate is between 0.3 to 2.0.
 25. A process according to claim19, 20 or 24 in which the alcohol is selected from: (a) methanol; (b)ethanol; (c) 2-propanol; (d) a combination of alcohols comprising two ormore of methanol, ethanol and 2-propanol.